Preheat the oven to 400°F. Line the bottom of a 10"x15" jelly roll pan with parchment paper. Place a kitchen towel on the counter and dust generously with confectioners sugar.
In a bowl, whisk together flour, baking powder and salt. Set aside.
Whisk in the buttermilk and oil in a small bowl and keep ready.
Beat the eggs in a large bowl until light and lemon colored. Add the sugar gradually, whisking the eggs continuously until the mixture is very thick and lemon colored.
Gently fold in the flour mixture. When the flour is almost but not quite uniformly distributed, whisk in the buttermilk mixture. Spread the batter evenly into the prepared pan.
Bake the cake until it's golden brown and springy to the tough, 12~14 minutes.
Remove the cake from the oven and invert it onto the prepared towel. Peel off the paper and trim the crusty edges of the cake, if necessary.
Use the towel to roll the warm cake up, from one short side of the rectangle to the other. Allow the cake to cool completely.
Whisk heavy cream, sugar and instant vanilla pudding mixture until soft peaks form.
Unroll the cooled cake, and spread the inside with raspberry jam. Top it with the whipped cream leaving the last 4" of the cake without the filling. This will keep the filling from oozing out when rolled.
Gently reroll the cake and place it seam side down on a serving plate. Dust the top with confectioners sugar before serving.